Disc brake having improved pad clip and pad return spring

ABSTRACT

A pad clip ( 12 ) for a disc brake includes a first part configured to engage a brake pad support bracket ( 2 ). The clip further includes a spring leg that is positioned to engage the brake pad ( 4 ) and apply a force to the brake pad that generates an axial friction force on the brake pad. The clip has a support for receiving a pad return spring ( 18 ) and the support for the pad return spring is positioned so that it holds the pad return spring such that the pad return spring applies a return force that is in substantial alignment with the axial friction force. The disc brake is further arranged so that the center of gravity of the brake pads lies between the pad abutment force and the axial friction force.

This application is a national stage of PCT/US03/020416 pursuant to 35USC §371, having an international filing date of Jun. 30, 2003, andclaims the benefit of U.S. Provisional Application 60/391,968, which wasfiled on Jun. 28, 2002.

TECHNICAL FIELD

This invention relates to the art of disc brakes. In particular, theinvention relates to the art of structures used to generate forces tocontrol the motion of brake pads and to support return springs in discbrakes.

BACKGROUND ART

Disc brakes typically employ one or more springs to urge the disc brakepads away from each other when braking pressure is released to avoiddrag on the rotor. Many different shapes have been used for thesesprings, and a typical spring is a V-shaped wire that attaches to thetop of the pad plate. This spring is nested between the caliper bodybridge and the rotor. The V-spring attachment requires a small hole tobe drilled into the edge of the pad plate, which is a costly operation.The wire form V-spring itself is expensive because it requires the wireto be bent at different angles and in different shapes.

In many applications the pad abutments are below the V-spring attachmentto the pad. In these cases, the function force between the pad abutmentand pad clips prevent the pad from moving away from the rotor inparallel fashion. Typically the top of the pad moves away while thebottom of the pad remains in contact with the rotor.

In many instances, the V-spring is trapped between the pad and theunderside of the caliper bridge. The spring legs must be sufficientlylong to remain engaged with the pad in all cases of pad to bridge gaptolerance. In many cases the V-spring will rub against the underside ofthe caliper bridge with a force large enough to cause the spring wire towear or to cause the caliper body slide force to increase.

SUMMARY OF THE INVENTION

In accordance with the invention, a pad return spring comprises aspring, preferably a coiled spring, that is held on the brake supportbracket by a pad clip. The pad clip attaches to the support bracket andincludes a rail that engages the pads for movement during brakingactions. The pad clip also includes a spring leg that applies a force tothe top of the pads to prevent rattle. The force applied by the springleg generates frictional forces on the pad between the spring leg andthe rail, and the return spring is positioned near this frictional forceto approximately align the force applied by the return spring with thefrictional forces and thereby prevent the pad from tilting byapplication of these forces.

Preferably the return spring is coiled and tubular, and the pad clipincludes a portion that receives the coiled spring to position it abovethe rotor. This location and shape reduce spring wear and help preventbuckling of the spring. The portion of the pad clip that receives thecoiled spring is preferably tubular with a longitudinal opening on oneside to prevent accumulation of debris and allow proper water drainage.The open side may be oriented, e.g., upward or downward depending on thecaliper design and packaging.

The pads themselves may include structure to help in positively locatingthe end of the spring on the pad. This may be a dimple that receives theend of a coiled spring or a protrusion engaged in the end of the spring.

The pad clip may include an anchor for the spring that is centrallylocated with respect to the pad movement. This allows the spring to beanchored to the clip such that the outward forces on the pads areproduced relative to a defined position on the support bracket and notrelative to the other pad. As well, this allows either the use of asingle return spring or two separate return springs. The use of tworeturn springs allows two distinct return spring forces, which may benecessary for proper caliper function.

Accordingly, it is an object of this invention to provide a unique padclip that supports a return spring for applying selected forces to discbrake pads to return them to rest positions upon relaxation of brakingforces.

It is a further object of the invention to provide a unique pad clip incombination with a coiled return spring that engages disc brake pads andurges the pads away from a disc brake rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view showing a disc brake system with a pad clipand return spring according to the invention.

FIG. 2 is a partial top plan view of a portion of a disc brake systemshowing the pad clip and return spring of the invention assembled.

FIGS. 3 and 4 are partial side views showing the engagement between acoiled return spring and a brake pad.

FIGS. 5 and 6 show alternate designs for the pad clip.

FIG. 7 is a partial perspective view of a pad clip in accordance withthe invention showing the portion that supports the return spring.

FIGS. 8 and 9 are partial cross sections of the pad clip shown alternatemethods of engaging a return spring.

FIG. 10 is a partial side view of a disc brake showing a secondembodiment of the inventive pad clip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the FIG. 1 of the drawings, a disc brake includes asupport bracket 2 that carries brake pads 4, as is known in the art.Only one of the pads is shown in FIG. 1, but it is understood that discbrakes generally include two such pads. The support bracket may includea rail 6 that engages a groove 8 in each pad to support the pads on thebracket. Each pad includes a friction brake material 10 attached to theface of the pad for engaging a brake rotor (see FIG. 2) during braking.

A pad clip 12 in accordance with the invention includes several featureswhereby it can be placed on the support bracket to prevent rattle of thepads and to support a return spring in an advantageous position. Thepreferred pad clip shown in FIG. 1 is made of relatively thin metal(e.g. steel) and is formed to provide a clip rail 14 that conforms tothe shape of the rail 6 so that the clip fits easily onto the supportbracket 2. If the support bracket were to have a feature other than therail 6 as shown, then the clip would be designed to cooperate with thatfeature. As well, of course, the clip could be designed to fit on thesupport bracket shown without engaging the rail 6.

The pad clip provides a spring leg 16 that is configured to engage thetops of the brake pads and apply a downward force on the pads to preventrattle of the brake pads. The spring leg is shown as comprising twospaced parts, but it will be appreciated that it could be a continuouspart extending across the entire clip or only a portion thereof, orseveral distinct, spaced parts.

The pad clip 12 includes structure for supporting a pad return spring18. In the preferred embodiment, the return spring 18 is a coiledspring, which provides a force in the axial direction (e.g., thedirection of movement of the pads) urging the pads to a rest position.The preferred support structure comprises a tubular support 20 thatextends outwardly from the clip rail 14 and generally adjacent the cliprail 14. The pad clip is preferably formed of thin metal, and thetubular support is formed by a curved flap of the metal, the flap beingattached to the remainder of the clip.

The tubular support is arranged to position the spring 18 between thedrake pads 4 such that the force applied by the spring to the pads isaligned with the frictional forces on the pad that are applied to thegroove 8. These frictional forces arise between the groove 8 and theclip rail 14 as a result of the downward force applied by the spring leg16. A frictional force also arises between the spring leg and the top ofthe pad where it engages the spring leg. Thus, there are frictionalforces applied to the top of the pad and to the groove that are overcomeby the spring 18 when brake pressure is relaxed. By positioning thespring between these forces, there is no net torque arising from theforces that would tend to rotate the pad and cause it to bind up.

FIG. 2 illustrates how the clip is attached to the support bracket 2with the brake pads 4 on opposite sides of the rotor 22.

FIGS. 3 and 4 illustrate a feature of the invention whereby the brakepads are configured to include a feature that engages the return spring.In FIG. 3, that feature is a protrusion 24 that engages a centralopening in the return spring. In FIG. 4, the feature is a depression, orhollow, 26 that receives the end of the spring.

FIGS. 5 and 6 show alternate embodiments of the tubular support 20. InFIG. 5, the tubular support 20 includes a longitudinal opening 28 on thebottom of the tubular support. This opening allows water to drain anddebris to drop out. It will be appreciated that the location of thelongitudinal opening depends on the ultimate orientation of the supportbracket and the overall configuration of the brake. Thus, FIG. 6 showsan embodiment wherein the longitudinal opening 28′ is at the top of thepad clip. As well, the opening 28 need not extend the entire length ofthe tubular support and may include other features, such as a screen orthe like to prevent entry of debris while allowing water to drain.

In accordance with a further feature of the invention, the return springcan be attached to the support 20 such that the forces applied by thereturn spring are controlled. In the embodiment shown in FIG. 7, thesupport 20 is provided with a tab 30 that engages the return spring asillustrated in FIGS. 8 and 9. The tab is conveniently formed of thesidewall of the tubular support, but may be formed in other ways or be aseparate element. Engagement between the tab 30 and the return spring 18(or springs) causes the force applied by the spring to be applied to thepad clip, as opposed to the other pad. Thus, in the embodiments shown inFIGS. 7, 8, and 9, the spring applies a force to a respective pad at oneend and to the tab 30 on the pad clip at the other. This allows theforces applied to the pads to be predetermined. In some cases, it may bedesirable for the forces to be equal, but in other cases it is desirablefor the forces to be different. Either situation can be addressed byappropriately setting the length or spring characteristics of the returnspring or springs.

FIG. 8 illustrates a configuration wherein the tab 30 engages anintermediate part of the return spring 18, as by engaging a portion ofthe helical coils. FIG. 9 illustrates an alternate embodiment whereintwo separate springs, 18 and 18′ are utilized. In the embodiment of FIG.8, the axial location of the coil engaged by the tab determines therelative strengths of the two parts, and in the embodiment of FIG. 9 therespective characteristics of each of the springs will determine therelative strengths. This allows the forces applied to the pads to bepredetermined.

It will be appreciated that the pad clip 12 may be used without thereturn spring. In one use, the pad clip is provided whereby the springleg 16 applies a force as discussed above to prevent rattle but thereturn spring is not used. The tubular support 20, however, acts as astop for the two brake pads and limits their movement toward each other.This has the advantage of maintaining the separation of the pads duringshipment, which facilitates final assembly of the brake system becauseit facilitates placement of the sub-assembly onto the rotor. This avoidsthe necessity of placing a dummy rotor between the pads during shipmentand the step of removing the dummy rotor at the final assembly location.

FIG. 10 shows another embodiment of the pad clip 12. In this embodiment,the use of the return spring 18 is optional because the primary functionof the pad clip is to apply a downward (in the direction of FIG. 10)force that urges the pad toward the support bracket 2. That forcegenerates an axial friction force, as discussed above, between thespring leg 16 and the top of the pad and between the pad groove orprojection and the clip rail or channel. It will be appreciated that thedesign of the support bracket shown in FIG. 10 utilizes a channel 32instead of a rail and that the pad 4 utilizes a projection 34 thatengages in the channel 32. In this design, the force on the brake padgenerated during braking operations is applied at a surface 36 of thesupport bracket 2. Thus, the brake pad has a complementary surface 40(see FIG. 1) that engages surface 36 whereby the pad abutment force isapplied at 36.

It will be appreciated that in this embodiment the pad abutment force isresisted at a location substantially below the center of gravity of thebrake pad 4, which is indicated by the circle at 38. Further, thefrictional force applied by the spring leg to the top of the brake padis near or somewhat above the center of gravity 38. To prevent tiltingof the brake pad during non-braking, it is desirable for the structureto provide that the frictional forces generated by the pad clip on thebrake pad are applied at approximately the level of the center ofgravity of the brake pad or above the level of the center of gravity byno more than twenty-five percent (25%) of the average height of the pad.This construction substantially reduces the tilt of the pad duringnon-braking by reducing the torque tending to tilt the pad about atangential axis resulting from the radial separation of forces resultingfrom inertia of the pad during movement of the vehicle in thenon-braking condition and the frictional resistance to movement appliedby the pad clip. (Note that radial and tangential directions aredetermined with reference to the rotor and the axial direction is thedirection of the wheel axle.)

The design shown in FIG. 10 is particularly advantageous because theabutment forces applied in the tangential direction during braking arebelow the center of gravity of the brake pad, while the frictionalforces generated by the pad clip in the axial direction are at orslightly above the center of gravity of the brake pad. This distributionof the forces has been found to be highly advantageous. The reduce padtilt substantially, which reduces brake jutter.

Modification within the scope of the appended claims will be apparent tothose of skill in the art.

1. A pad clip comprising a portion adapted to engage a brake pad supportbracket, an elongate clip rail configured to engage a brake pad andguide said brake pad in an axial direction, a spring leg positionedabove said clip rail and configured to engage a brake pad and apply aforce to said brake pad to generate an axial frictional force on saidbrake pad between said brake pad and said clip rail, and a support for apad return spring, wherein the support for the pad return spring ispositioned horizontally adjacent said clip rail with respect to saidbrake pad support bracket and includes an opening for receiving said padreturn spring within said support, where said support is positionedbelow the engagement between said spring leg and said brake pad to holda pad return spring such that the pad return spring applies a returnforce to said brake pad in substantial alignment with said axialfriction force.
 2. A pad clip according to claim 1 wherein said supportfor a pad return spring comprises a tubular component extending in theaxial direction.
 3. A pad clip according to claim 1 made of foldedmetal.
 4. A pad clip according to claim 1 further comprising a padreturn spring engaged in said support and extending in said axialdirection.
 5. A pad clip wherein said pad return spring comprises acoiled spring.
 6. A pad clip wherein said support includes means forrestricting the axial movement of said pad return spring.
 7. A pad clipwherein said support comprises a tubular element forming a cavityreceiving said pad return spring and said means for restrictingcomprises a tab extending into said cavity.
 8. A pad clip wherein saidpad return spring comprises at least two coiled springs.
 9. A pad clipcomprising a first portion adapted to engage a brake pad supportbracket, an elongate clip rail configured to engage opposed brake padsand to guide said brake pads for motion in an axial direction, a springleg positioned to engage said brake pads and apply a force to said brakepads to generate an axial frictional force on said brake pads betweensaid brake pads and said clip rail, and a second portion positionedadjacent said clip rail and configured to extend axially between saidopposed brake pads to maintain a minimum separation of said brake padsby engagement with said brake pads, wherein said second portion islocated below the engagement between said spring leg and said brakepads.
 10. A pad clip according to claim 9 wherein said second portioncomprises a support for a pad return spring.
 11. A pad clip according toclaim 10 in further combination with said pad return spring.
 12. A padclip wherein said pad return spring comprises a tubular coiled springextending in said axial direction.
 13. A disc brake comprising a supportbracket, at least one brake pad having a center of gravity, and a padclip, wherein said support bracket comprises means for receiving a padabutment force, said means for receiving being displaced from saidcenter of gravity in a radial direction, and said pad clip applies aforce to said brake pad that generates an axial frictional force alignedwith said center of gravity or displaced therefrom in a radial directionopposite that of said means for receiving by a distance that is lessthan twenty five percent of the height of the brake pad, wherein saidpad abutment force is radially spaced from the axial frictional forceand is located below the center of gravity.
 14. A disc brake accordingto claim 13 wherein said pad clip further comprises a support for a padreturn spring, wherein said support is located below said axial frictionforce.
 15. A disc brake according to claim 14 wherein said support isconfigured to support the pad return spring in a position such that itapplies a pad return force in substantial alignment with said axialfriction force.
 16. A disc brake according to claim 15 wherein saidsupport is a tubular element forming a cavity for receiving said padreturn spring.
 17. A disc brake according to claim 13 wherein said padclip includes means between opposed brake pads for limiting the movementof said pads toward each other.
 18. A disc brake wherein said supportcomprises a tubular element forming a cavity receiving said pad returnspring and said means for restricting comprises a tab extending intosaid cavity.
 19. A disc brake wherein said pad return spring comprisesat least two coiled springs.